1. Field of the Invention
This invention relates generally to the balancing of a motor vehicle wheel rim and tire, and in particular to an apparatus able to directly determine any shape imperfections in the wheel when the wheel is positioned on a self-centering unit of a tire removal machine.
2. Discussion of Related Art
The wheel rim and/or tire part of a vehicle wheel can present various shape imperfections or defects which can disturb vehicle travel during wheel rotation.
The most common imperfections or defects include the following: ovalized wheel rim shape; conical wheel rim shape due to slight diameter differences in the bead retaining flanges; ovalized tire shape: and conical tire tread shape.
The same tire can also have irregular rigidity (or deformity), due to the position and nature of the joints between its inner bands.
The defects or imperfections lead to irregular tire rolling, thus disturbing vehicle travel and decreasing travelling comfort.
The negative effects of the aforesaid shape defects, if present in both the tire and wheel rim, can often be greatly reduced or even totally eliminated by suitably positioning the tire relative to the wheel rim, in order to compensate the defects.
The main object of this invention is to provide an apparatus able to determine imperfections or defects when a wheel is positioned on the self-centering unit of a tire removal machine, so that account can be taken thereof on removing and remounting the tire.
The object is attained within the framework of a constructionally simple, reliable and low-cost solution usable on existing tire removal machines in general and on tire removal machines of new construction, by virtue of an apparatus having the characteristics defined herein.
The apparatus of the invention comprises at least one measurement unit to be associated with the self-centering unit of a tire removal machine, in order to occupy a rest position in which it lies outside the operational region of the self-centering unit and a working position in which it can assume a first measuring configuration in which it is in light contact with the bead retaining flange of the wheel rim of the wheel at that moment mounted on the moving self-centering unit, and a second configuration in which it is in light contact with the tread of the tire of the mounted wheel, the measurement unit being connected to a system for collecting and displaying the data obtained.
When the at least one measurement unit, described in detail hereinafter, is in a first measuring configuration, it measures any wheel rim ovalization, whereas when in the second measuring configuration it measures any ovalization of the tire tread.
According to a preferred embodiment, the at least one measurement unit is also equipped with means which, simultaneously with the measurement of any wheel rim and tread ovalization, also measure any conicity thereof.
Two measurement units are preferably provided, of which one effects said wheel rim measurements and the other effects the same measurements on the tire tread.
A third measurement unit can be provided to determine any tire flexibility or deformity or irregularities.
Goniometer means, also suitably connected to the collection and display system, are preferably associated with the measurement units in order to provide strict correlation between the error data determined by the measurement units and the respective angular positions.
The apparatus is preferably mounted on a structure which is to be located to the rear of the vertical-axis self-centering unit of a tire removal machine and has a vertical plane of symmetry containing a vertical axis.